KR20060052702A - Composite surface on a steel substrate - Google Patents

Abstract

A composite surface having a thickness from 10 to 5,000 microns comprising a spinel of the formula Mnx Cr3_xO4wherein x is from 0.5 to 2 and oxides of Mn, Si selected from the group consisting of MnO, MnSiO3, Mn2SiO4 and mixtures thereof which are not prone to coking and are suitable for hydrocarbyl reactions such as furnace tubes for cracking.

Description

COMPOSITE SURFACE ON A STEEL SUBSTRATE}

The present invention relates to composite surfaces useful on steel substrates, in particular stainless steels. The present invention provides a composite surface on a steel substrate that provides enhanced material protection (eg, protects the steel substrate or matrix). This composite surface reduces coking in applications where steel is exposed to hydrocarbon environments at elevated temperatures. Such stainless steels are used in a variety of applications, particularly in pyrolysis processes such as the treatment of hydrocarbons and specifically the dehydrogenation of alkanes to olefins (eg ethane to ethylene); Reaction tubes for hydrocarbon decomposition; Or in a reaction tube for steam cracking or steam reforming reactions.

It has been known for quite some time that the surface composition of a metal alloy can have a significant impact on the usefulness of the metal alloy. Methods are known for treating steel to produce a layer of iron oxide that is easily removed. Also known are methods of treating steel to enhance wear resistance. Until now, the use of stainless steel has been dependent on the protection produced by the chromia surface (eg against other forms of corrosion and material degradation). As far as the applicant knows, there are not many techniques for treating steel to significantly reduce coking in the hydrocarbon manufacturing process. Little has been written about the shape of the surface that significantly reduces coking in the hydrocarbon manufacturing process.

Experimental results have been made in the nuclear industry that spinels similar to the present invention can be produced as the outer surface of stainless steel. However, these spinels tend to be thermomechanically unstable and split into thin layers. This is an easy limitation to teach against commercial use of such surfaces. Such surfaces have been evaluated for use in the nuclear industry but have not been used commercially as far as applicants know.

In the petrochemical industry, due to its thermo-mechanical limitations, spinels similar to those used in the present invention are generally considered to be less protective than chromia. It is also believed that in view of coke formation, spinels similar to those used in the present invention are considered to be less catalytically inert than chromia. Because of this teaching, as far as applicants know, such spinels are neither produced nor recommended for use in the petrochemical industry.

Canadian Patent No. 1,028,601, issued to Exxon Research and Engineering Company on March 28, 1978 to Bagnoli et al., Contains 1.25 to 2 percent by weight of manganese and residual iron. High nickel (e.g., 36-38% by weight) -high chromium (e.g., 23-27% by weight) steels. The surface of this steel can be oxidized in steam at temperatures in the range of 500 ° F. (160 ° C.) to about 2000 ° F. (1093.3 ° C.). This patent teaches that there is a protective film of manganese and chromium oxide (chromium oxide or chromium Cr ₂ O ₃ ) formed on the inside of the pipe. This reference teaches differences from the formation of chromium-manganese spinels (MnCr ₂ O ₄ ). Moreover, this reference did not teach their use as the formation of oxides of manganese and / or silica or as the outer coating of composite surfaces, selected from the group consisting of MnO, MnSiO ₃ , Mn ₂ SiO ₄ and mixtures thereof.

Summary of Japanese Patent No. 57019179B includes Cr 16-19% by weight, 0.75-1.25% by weight Mo, optionally 0.12% by weight copper and carbon, 0.01% by weight or less Ni, 0.1% by weight Si and Mn, 0.01% by weight S Teaching ferritic stainless steel containing; This is coated with a MnCr ₂ O _4, or Cr ₂ O ₃ thin film having a thickness of 50nm or more, which contains only a MnCr ₂ O ₄ with MnSiO _3. This summary does not teach a composite thin film of the present invention having an outer coating of oxides of Mn and / or Si, selected from the group consisting of MnO, MnSiO ₃ , Mn ₂ SiO ₄ and mixtures thereof. The resulting surface has improved corrosion resistance. References are silent about surface corrosion resistance.

U.S. Patent No. 5,630,887, issued to Novaco Chemicals Limited (now Nova Chemicals Corporation), issued to Benum et al. On May 20, 1997, contains about 15-25 weight percent manganese and about 60-75 weight percent chromium. Teaching method of stainless steel to produce a surface layer having a total thickness of about 20 to 45 microns containing. This patent clearly requires the presence of both manganese and chromium in the surface layer but does not teach spinel or Mn oxides (eg MnO) and / or manganese and silicon oxides (eg MnSiO ₃ and Mn ₂ SiO ₄ ). .

US Patent No. 6,436,202 B1, assigned to Nova Chemicals (International) Societe Anonym, issued to Benum et al. On August 20, 2002 and WO 02/22910; WO 02/22908 and WO 02/22905 teach higher chrome steels treated in an oxidizing atmosphere to produce a surface predominantly spinel of formula Mn _x Cr _{3 - x} O ₄ , where x is 0.5 to 2. This reference does not teach a surface additionally containing Mn, Si, oxides selected from the group consisting of MnO, MnSiO ₃ , Mn ₂ SiO ₄ and mixtures thereof.

The present invention seeks to provide a novel surface structure with good caking resistance.

Disclosure of the Invention

The present invention relates to 90 to 10% by weight, preferably 40 to 60% by weight of a compound of the formula Mn _x Cr _{3 - x} O ₄ , wherein x is 0.5 to 2, and MnO, MnSiO ₃ , Mn on a steel substrate _It provides a surface having a thickness of 10 to 5,000 microns, containing 10 to 90% by weight, preferably 60 to 40% by weight, of oxides of Mn and Si selected from the group consisting of ₂ SiO ₄ and mixtures thereof. Cr ₂ O ₃ is preferably absent but, if present, is present in an amount of less than 5% by weight, preferably less than 2% by weight and most preferably less than 0.5% by weight of the surface.

The invention additionally provides 90 to 10% by weight of a compound of the formula Mn _x Cr _3-x O ₄ , wherein x is 0.5 to 2, and Mn selected from the group consisting of MnO, MnSiO ₃ , Mn ₂ SiO ₄ and mixtures thereof And applying a composition containing 10 to 90% by weight of an oxide of Si, the composition being assumed to contain less than 5% by weight of Cr ₂ O _3, to at least a portion of the steel substrate. Applying the composition to at least 70% of the substrate surface by a method selected from the group consisting of explosion spraying, cement packing, hard facing, laser cladding, plasma spraying, physical vapor deposition techniques, flame spraying and electron beam thermal evaporation. To 5,000 microns thick.

In a further embodiment, the present invention provides a stainless steel article such as a pipe or tube, reactor or heat exchanger having at least a portion of the inner surface containing the composite surface.

In a further embodiment, the present invention provides for the use of such a device, especially in environments where coking is likely to occur, such as hydrocarbon decomposition or steam reforming reactions.

1 is an SEM micrograph of Example 2. FIG.

2 is an X-ray diffraction spectrum of Example 3.

3 is a plot of the results from Example 4. FIG.

Best Mode for Carrying Out the Invention

In many industries and in particular in the chemical industry, stainless steel substrates are used to produce devices (eg furnace tubes, steam reforming reactors, heat exchangers and reactors) used in harsh environments that can result in coking of stainless steel surfaces. In the ethylene furnace industry, this furnace tube may be a single tube or a device for forming a coil and a plurality of tubes, which may be easy to weld together to form (coke) the coke.

The substrate can be any material to which the composite coating will bind. The substrate may be stainless steel or carbon steel, which may be selected from the group consisting of forged stainless steel, austenitic stainless steel and HP, HT, HU, HW and HX stainless steels (heat resistant and nickel based alloys). The substrate may be high strength low alloy steel (HSLA) and may be high strength structural steel or ultra high strength steel. Such steel classifications and compositions are well known to those skilled in the art.

In one embodiment, the stainless steel, preferably heat resistant stainless steel, typically contains 13 to 50% by weight, preferably 20 to 50% by weight, most preferably 20 to 38% by weight of chromium. The stainless steel may additionally contain 20 to 50% by weight, preferably 25 to 50% by weight, most preferably 25 to 48% by weight and possibly 30 to 45% by weight of Ni. The remaining component of the stainless steel is substantially iron.

The invention can also be used with nickel and / or cobalt based extreme austenitic high temperature alloys (HTAs). Typically this alloy contains nickel or cobalt in major amounts. Typically nickel based hot alloys comprise about 50 to 70 weight percent Ni, preferably about 55 to 65 weight percent; About 20 to 10% Cr; About 20 to 10 weight percent Co; And about 5-9 weight percent Fe, and at least one of the trace elements described below in order to make the composition 100 weight percent. Typically cobalt based hot alloys comprise Co 40-65 wt%; Cr 15-20 wt%; Ni 20-13 weight%; It contains less than 4% by weight of Fe and one or more trace elements shown below in residual amounts and up to 20% by weight of W. The total amount of components is 100% by weight.

In some embodiments of the invention, the substrate further comprises at least 0.2% to 3% by weight, typically 1.0% to 2.5% by weight or less, preferably 2% by weight or less manganese; 0.3 to 2 weight percent, preferably 0.8 to 1.6 weight percent, typically less than 1.9 weight percent Si; Less than 3 weight percent, typically less than 2 weight percent titanium, niobium (typically 2.0 weight percent, preferably less than 1.5 weight percent niobium) and all other trace metals; And carbon in an amount of less than 2.0% by weight.

The surface has a thickness of about 10 to 5,000 microns, typically 10 to 2,000 microns, preferably 10 to 1,000 microns and possibly 10 to 500 microns. Typically the substrate surface covers at least about 70%, preferably 85%, most preferably at least 95% and possibly at least 98.5% of the surface of the stainless steel substrate.

The surface and the composition used to prepare the surface are 90 to 10% by weight, preferably 60 to 40% by weight, most preferably 45 to 55% by weight of the spinel (e.g. Mn _x Cr _{3 - x} O ₄ , where x is 0.5 to 2), and 10 to 90% by weight of oxides of Mn and Si selected from the group consisting of MnO, MnSiO ₃ , Mn ₂ SiO ₄ and mixtures thereof, preferably 40 to 60% by weight, most preferably 55 to It contains 45% by weight.

If the oxide has a nominal stoichiometry of MnO, Mn may be present on the surface in an amount of 1 to 50 atomic percent. When the oxide is MnSiO ₃ , Si may be present on the surface in an amount of 1 to 50 atomic percent. If the oxide is Mn ₂ SiO ₄ , Si may be present in the surface at 1 to 50 atomic percent.

The surface and the composition used for the preparation of the surface contain less than 5% by weight, preferably less than 2% by weight and most preferably less than 0.5% by weight of Cr ₂ O ₃ . Most preferably Cr ₂ O ₃ is absent from the surface or the composition used to prepare the surface.

The composition used to prepare the surface may be a surface of a metal substrate or a selected portion of a selected substrate surface using conventional deposition processes (eg, interior or exterior coke, such as heat exchangers, where the interior tends to be coking conditions such as furnaces). May be applied to the outside), which tends to be liable to chemical conditions. Such substrate may be any metal to which the composition is attached, preferably to be bonded (chemically). The substrate may be stainless steel or carbon steel, which may be selected from the group consisting of forged stainless steel, austenitic stainless steel, and HP, HT, HW and HX stainless steel, heat resistant steel, and HTA nickel and cobalt based alloys. The substrate is a high strength low alloy steel (HSLA); It can be high strength structural steel or ultra high strength steel. The substrate may also be a high temperature material, including but not limited to superalloys and intermetallic alloys. Classification and composition of such steels are known to those skilled in the art.

Components of the surface composites that may be present in the form of powders include explosion spraying, cement packing, hardening, laser cladding, plasma spraying (eg, low pressure plasma spraying), physical vapor deposition techniques (cathodic arc sputtering, DC, RF, electron tubes). PVD), flame spraying (e.g., high pressure / high speed oxygen fuel (HP / HVOF)) and electron beam heating deposition can be used per se as a coating composition. Combinations of these methods can also be used. Typically a powder with the desired composition is applied to the substrate.

The composite surface may also be placed in a heating process (which may be concurrent or sequential with the deposition process) at a temperature that will result in the formation of a layer or alloy of the target surface composition. In some cases, there may be elemental diffusion from the substrate into the composite surface coating. There may be a sequential finishing / processing step that realizes the properties of the selected residue. For example, if mechanical robustness is the desired property, it may include materials that can interdiffuse into the matrix and conform to the coefficient of thermal expansion (CTE) in the deposition step (eg, composition). Relying on outward diffusion from steel to spinel is limited and may not provide a material that can wet the surface composition. One factor limiting this type of treatment is the temperature at which the substrate can withstand physical integrity and maintain its properties.

Steel substrates may be forged, rolled or cast. In one embodiment of the invention, the steel is in the form of a pipe or tube. The tube has an inner composite surface according to the invention. These tubes are isobutane in the presence of a catalyst or typically petrochemical processes such as the decomposition of hydrocarbons and specifically the decomposition reactions of ethane, propane, butane, naphtha and gas oils or mixtures thereof. ) from the typically C _{3 -6,} preferably such as isobutylene can be used for the steam reforming reaction of hydrocarbon C _{4 -6.} Stainless steel may be present in the form of a reactor or vessel having an inner composite surface according to the invention. The stainless steel may be present in the form of a heat exchanger in which one or both of the inner and outer surfaces are composite surfaces according to the invention. Such heat exchangers can be used to control the enthalpy of the fluid passing over or through the heat exchanger.

Particularly useful uses for the composite surfaces of the present invention are those used to decompose alkanes (eg, ethane, propane, butane, naphtha and gas oils, or mixtures thereof) to olefins (eg, ethylene, propylene, butene, etc.). Old pipe or no pipe. Generally in such a process, the feed (e.g. ethane) typically has an outer diameter in the range of 1.5 to 8 inches (e.g. a typical outer diameter is 2 inches (about 5 cm); 3 inches (about 7.6 cm); 3.5 inches (about 8.9 cm) Supplied in gaseous form to a tube, pipe, or coil that holds 6 inches (about 15.2 cm) and 7 inches (about 17.8 cm). The pipe or pipe is passed through a furnace which is generally maintained at a temperature of about 900 ° C. to 1100 ° C., and the exhaust gas is generally about 800 ° C. to 900 ° C. As the feed passes through the furnace, it feeds off hydrogen (and other byproducts) and is unsaturated (eg ethylene). Typical operating conditions such as temperature, pressure and flow rate are well known to those skilled in the art.

The invention will now be illustrated by the following non-limiting examples.

Example 1: SEM / EDS analysis of the coating

A large number of films were prepared on a substrate of stainless steel. Scanning electron microscopy / energy dispersion spectroscopy (SEM / EDS) analysis of the composition was performed using a Hitachi S-2500 SEM with Oxford EDS system. The results of EDS analysis of typical coatings are shown in Table 1.

EDS  Coating composition (% by weight) by analysis Film system element MnCr ₂ O ₄ MnO-Mn MnO-Mn-Si Mn 24.1% 77.0% 15.8% Cr 45.9% - - O 29.0% 22.7% 46.4% Si 0.2% 0.2% 33.6% Al 0.5% 0.1% 3.7% Zr 0.5% - - Ni - - - Fe - - - Etc - - 0.6% 100% 100% 100%

Example  2: Spinel MnCr ₂ O ₄  Metallographic analysis cross sections of the base coating (at 100X and 300X magnifications) SEM  Photomicrograph

Samples of austenitic stainless steel bearing the composite surface of the present invention were fixed to a metal microscope, polished and carbon coated using standard techniques, and imaged using a secondary electron microscope as shown in FIG. 1.

The figure clearly shows that there is a surface composition different from the substrate and that the composition is well bonded to the substrate via a bond-layer.

Example  3: Spinel MnCr ₂ O ₄  X-ray of the base film diffraction  analysis

X-ray diffraction analysis of the coating of the composition of the present invention on stainless steel was performed using a Bruker D8 X-ray diffractometer with a Cu source of X, equipped with a Goebel mirror, and a bright projection capability. FIG. 2 is an X-ray diffraction spectrum obtained at 40 KeV, 40 ma, showing a well bonded structure of the primary spinel structure Mn ₂ Cr ₂ O ₄ of the coating.

Example  4: coking Performance test  result

Laboratory scale quartz reactors were used to initiate coking rate performance testing of coating systems and comparative materials. This test provides a relative ranking of the coking tendency of materials under hydrocarbon vapor cracking conditions aimed at producing olefins, primary ethylene. When ethane was used as the hydrocarbon source, the test conditions used demonstrated the coating or surface resistance to the form of catalyzed coke (also known as island coke) basically. It is well known in the literature that surface materials such as Fe and Ni have a strong tendency of such catalyzed coke-forming, while ceramic materials such as alumina are inert. The results are shown in FIG. The test conditions were a steam: ethane ratio of 1: 3 (% by weight) at a reaction temperature of 800 ° C., a lag time of 2 seconds and a total test duration of 1 hour. The results shown in Table 2 show excellent resistance to catalytic coke-forming of the three coating systems shown in Table 1, compared to highly inert ceramic materials (alumina) and very catalytically-active Fe and Ni.

Sample Surface area Yield weight Coking rate (cm ² ) (mg) (mg / cm ² / hr) Al ₂ O ₃ -Control 4.25 0.1 0.02 MnCr ₂ O ₄ -based coatings 3.75 0.1 0.03 MnO-based film 2.69 0.2 0.07 Mn silicate-based coatings 3.00 0.1 0.03 Ni- control 3.69 4.7 1.27 Fe-control 3.55 75.9 21.37

The present invention extends the time for coke formation on surfaces exposed to hydrocarbons under reactive conditions and in particular the time between decoking in ethylene furnaces.

Claims (48)

90 to 10% by weight of a compound of the formula Mn _x Cr _{3 - x} O ₄ , where x is 0.5 to 2, and MnO, MnSiO ₃ , Mn ₂ SiO ₄ and mixtures thereof, applied onto a steel substrate A surface containing 10 to 90% by weight of selected oxides of Mn and Si, having a thickness of 10 to 5,000 microns, and containing less than 5% by weight of Cr ₂ O ₃ . The surface of claim 1, wherein at least 85% of the substrate surface is applied. The surface of claim 2, wherein the thickness is from 10 to 1,000 microns. 4. Surface according to claim 3, characterized in that it contains 40 to 60% by weight of the spinel and 60 to 40% by weight of oxides of Mn and Si selected from the group consisting of MnO, MnSiO ₃ , Mn ₂ SiO ₄ and mixtures thereof. . The surface of claim 4, wherein the Cr ₂ O ₃ is present in an amount of less than 2% by weight. The surface of claim 5, wherein the substrate is selected from the group consisting of carbon steel, stainless steel, heat resistant steel, HP, HT, HU, HW and HX stainless steel, and nickel or cobalt based HTA alloys. The surface of claim 6, wherein the substrate contains 13 to 50 weight percent Cr and 20 to 50 weight percent Ni. The method of claim 6, wherein the substrate is 50 to 70% by weight of Ni; 20 to 10 weight percent Cr; 20 to 10 weight percent Co; And 5 to 9% by weight of Fe. The method of claim 6, wherein the substrate is 40 to 65% by weight of Co; 15 to 20% Cr by weight; 20 to 13 weight percent Ni; Less than 4% Fe; And 20% by weight or less. The surface of claim 7, wherein the oxide is MnO. The surface of claim 7, wherein the oxide is MnSiO ₃ . The surface of claim 7, wherein the oxide is Mn ₂ SiO ₄ . The surface of claim 7, wherein the oxide is a mixture of MnO, MnSiO _3, and Mn ₂ SiO ₄ . The surface of claim 8, wherein the oxide is MnO. The surface of claim 8, wherein the oxide is MnSiO ₃ . The surface of claim 8, wherein the oxide is Mn ₂ SiO ₄ . The surface of claim 8, wherein the oxide is a mixture of MnO, MnSiO _3, and Mn ₂ SiO ₄ . The surface of claim 9, wherein the oxide is MnO. The surface of claim 9, wherein the oxide is MnSiO ₃ . The surface of claim 9, wherein the oxide is Mn ₂ SiO ₄ . The surface of claim 9, wherein the oxide is a mixture of MnO, MnSiO _3, and Mn ₂ SiO ₄ . 90 to 10% by weight of a compound of the formula Mn _x Cr _{3 - x} O ₄ , wherein x is 0.5 to 2, and an oxide of Mn and Si selected from the group consisting of MnO, MnSiO ₃ , Mn ₂ SiO ₄ and mixtures thereof A method for applying a composition containing at least 90% by weight to less than 5% by weight of Cr ₂ O ₃ to at least a portion of a steel substrate, wherein the composition is applied to at least 70% of the selected steel substrate surface by explosive spraying, cement packing, curing Applying by a method selected from the group consisting of hard facing, laser cladding, plasma spraying, physical vapor deposition techniques, flame spraying and electron beam thermal evaporation to provide a thickness of 0.1 to 5,000 microns. . The method of claim 22, wherein the composition covers at least 85% of the selected substrate surface. The method of claim 23, wherein the surface has a thickness of 10 to 1,000 microns. 25. The composition of claim 24, wherein the composition contains from 40 to 60 weight percent of the spinel and from 60 to 40 weight percent of oxides of Mn and Si selected from the group consisting of MnO, MnSiO ₃ , Mn ₂ SiO ₄ and mixtures thereof. Phosphorus, composition application method. The method of claim 25, wherein the Cr ₂ O ₃ is present in an amount of less than 2% by weight. 27. The method of claim 26, wherein the substrate is selected from the group consisting of carbon steel, stainless steel, heat resistant steel, HP, HT, HU, HW and HX stainless steel, and nickel or cobalt based HTA alloys. The method of claim 27, wherein the substrate contains 13-50 wt.% Cr and 20-50 wt.% Ni. The method of claim 27, wherein the substrate comprises 50 to 70 weight percent Ni; 20 to 10 weight percent Cr; 20 to 10 weight percent Co; And 5 to 9% by weight of Fe. The method of claim 27, wherein the substrate comprises 40 to 65 weight percent of Co; 15 to 20% Cr by weight; 20 to 13 weight percent Ni; Less than 4% Fe; And 20% by weight or less of W. The method of claim 28, wherein the oxide is MnO. 29. The method of claim 28 wherein the oxide is MnSiO ₃ . The method of claim 28, wherein the oxide is Mn ₂ SiO ₄ . The method of claim 28, wherein the oxide is a mixture of MnO, MnSiO _3, and Mn ₂ SiO ₄ . The method of claim 29, wherein the oxide is MnO. The method of claim 29, wherein the oxide is MnSiO ₃ . The method of claim 29, wherein the oxide is Mn ₂ SiO ₄ . The method of claim 29, wherein the oxide is a mixture of MnO, MnSiO _3, and Mn ₂ SiO ₄ . 31. The method of claim 30 wherein the oxide is MnO. 31. The method of claim 30, wherein the oxide is MnSiO ₃ . 32. The method of claim 30 wherein the oxide is Mn ₂ SiO ₄ . 31. The method of claim 30, wherein the oxide is a mixture of MnO, MnSiO ₃ and Mn ₂ SiO ₄ . A stainless steel pipe or tube having at least a portion of the inner surface containing the composite surface of claim 1. A stainless steel reactor, having at least a portion of an inner surface containing the composite surface of claim 1. A stainless steel heat exchanger having at least a portion of an inner surface containing the composite surface of claim 1. A method of pyrolysis of hydrocarbons comprising passing the hydrocarbons at elevated temperature through the stainless steel tube, pipe or coil of claim 43. 46. A method of changing the enthalpy of a fluid, comprising passing the fluid through the heat exchanger of claim 45. 45. A process for carrying out a chemical reaction in the stainless steel reactor of Claim 44.

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